1. Field of the Invention
The present invention relates to a synchronous machine controller having a power conversion unit for driving a synchronous machine.
2. Background Art
As well known in the art, when a synchronous machine having a permanent magnet as a field magnet is controlled with a synchronous machine controller having a power conversion unit such as an inverter, a phenomenon called “demagnetization” occurs in which the intensity of magnetization, that is, the magnetic flux, of the permanent magnet as a field magnet decreases with a rise in temperature due to current supply of an armature winding of the synchronous machine, iron loss of the synchronous machine itself, or the like. In addition, a phenomenon called “irreversible demagnetization” occurs in which the magnetic flux does not return to the state before the occurrence of magnetization when the temperature once exceeds an allowable temperature and then falls to the normal temperature. Accordingly, when controlling a synchronous machine having a permanent magnet as a field magnet, it is necessary to control at least the temperature of the permanent magnet so as to be lower than the allowable temperature at which irreversible demagnetization occurs. When only the current of the synchronous machine is controlled, the torque generated from the synchronous machine is lowered due to the demagnetization under the same current condition. However, it is difficult to directly mount a temperature sensor on the permanent magnet because of a space problem in a structure of the synchronous machine, protection of surroundings with a case, and the like. Most synchronous machines having a permanent magnet as a field magnet often have the permanent magnet inside a rotor, which makes it more difficult to mount a temperature sensor thereon. Accordingly, in order to control the temperature so as to be lower than the allowable temperature or to confirm a fall in torque due to the demagnetization, there is a demand for techniques of indirectly measuring or estimating the temperature of the permanent magnet or the magnetic flux correlated with the temperature of the permanent magnet using any method.
Therefore, for example, in a rotary electric machine controller disclosed in JP-A-2010-110141, a magnetic flux interlinked with an armature winding from a permanent magnet as a field magnet is acquired on the basis of information on current, temperature, and rotational velocity obtained from sensors such as a current sensor for detecting current flowing between an inverter device and the armature winding of a motor generator, a temperature sensor for detecting the temperature of the armature winding so as to correct a resistance value of the armature winding, and a magnetic pole position sensor for detecting the magnetic pole position of the field magnet.
For example, in a motor driving device disclosed in JP-A-2005-51892, a q axis voltage control value when demagnetization does not occur in a permanent magnet in control using rotational two-axis coordinate (d-q axes) transform is stored in a map and a demagnetization value is calculated on the basis of the q axis voltage control value which is an output of a PI controller when current of a motor is controlled by proportional-integral (PI) control, the q axis voltage control value stored in the map when demagnetization does not occur in the permanent magnet, and a rotational angular velocity ω.
For example, in a demagnetization detecting method of a permanent-magnet electric motor disclosed in JP-A-2005-192325, a step ST1 of measuring a rotational velocity, a current, and a voltage, a step ST3 of estimating the temperature of a winding on the basis of the measured values of the rotational velocity, the current, and the voltage, a step ST4 of estimating the resistance of the winding on the basis of the estimated value of the winding temperature, a step ST5 of estimating the temperature of a rotor magnet portion on the basis of the estimated value of the winding temperature, a step ST6 of estimating a normal value of an induced voltage on the basis of the estimated value of the winding temperature, a step ST7 of estimating an actual value of the induced voltage on the basis of the estimated value of the winding resistance, and a step ST8 of comparing the normal value of the induced voltage coefficient and the actual value, which are estimated in the previous two steps, with each other and determining that demagnetization occurs when the difference therebetween is larger than a predetermined threshold value are sequentially carried out to determine a demagnetization state of the rotor magnet portion.
However, in the rotary electric machine controller disclosed in JP-A-2010-110141, since the resistance value of the armature winding corrected on the basis of the temperature sensor for detecting the temperature of the armature winding is used to acquire the magnetic flux interlinked with the armature winding from the permanent magnet as the field magnet by the use of a flux observer, the temperature sensor for detecting the temperature of the armature winding is necessary and thus there is a problem in that the number of constituent components of the controller increases.
In the motor driving device disclosed in JP-A-2005-51892, it is possible to determine whether demagnetization occurs, but a method of acquiring the absolute value (quantity) of a magnet temperature or a magnet flux is not disclosed and it is necessary to set a d-q axis current command to be equal before and after occurrence of demagnetization so as to determine whether demagnetization occurs. Accordingly, when demagnetization occurs, a decrease in torque due to the demagnetization is corrected by calculating and correcting the demagnetization value after determining that demagnetization occurs, and thus there is a problem in that the torque generated from the motor is lower than a desired torque (command value) until it is determined that demagnetization occurs.
In the demagnetization detecting method of a permanent-magnet electric motor disclosed in JP-A-2005-192325, a ratio of a temperature rise of the armature winding and a temperature rise of the rotor permanent magnet is experimentally calculated in advance and the temperature of the permanent magnet is estimated on the basis of the temperature of the armature winding. However, since a thermal time constant is greatly different between the armature winding and the permanent magnet and other factors such as operating conditions of an electric motor or cooling performance have influence, there is a problem in that it is difficult to unmistakably calculate the temperature rise of the rotor permanent magnet relative to the temperature rise of the armature winding and it is not easy to accurately estimate the magnet temperature on the basis of the temperature of the armature winding under various conditions.